Note 4 - Loans Receivable and Related Allowance for Loan Losses - Impaired Loans by Class (Details) - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
Mar. 31, 2019	Mar. 31, 2018	Dec. 31, 2018
Impaired loans with specific allowance, unpaid principal balance	$ 141	$ 83	$ 80
Impaired loans with specific allowance, recorded investment	141	83	80
Related allowance	70	6	12
Impaired loans with specific allowance, average recorded investment	110	83	81
Impaired loans with specific allowance, interest income recognized in period	1	1	2
Impaired loans with specific allowance, cash basis interest recognized in period	1	1	2
Impaired loans with no specific allowance, unpaid principal balance	454	1,347	500
Impaired loans with no specific allowance, recorded investment	379	1,235	388
Impaired loans with no specific allowance, average recorded investment	383	1,534	1,350
Impaired loans with no specific allowance, interest income recognized in period	3	2	235
Impaired loans with no specific allowance, cash basis interest recognized in period	3	2	152
Residential Portfolio Segment [Member]
Impaired loans with specific allowance, unpaid principal balance	73	75	74
Impaired loans with specific allowance, recorded investment	73	75	74
Related allowance	7	6	12
Impaired loans with specific allowance, average recorded investment	73	75	74
Impaired loans with specific allowance, interest income recognized in period	1	1	2
Impaired loans with specific allowance, cash basis interest recognized in period	1	1	2
Impaired loans with no specific allowance, unpaid principal balance	382	456	427
Impaired loans with no specific allowance, recorded investment	307	344	315
Impaired loans with no specific allowance, average recorded investment	311	347	334
Impaired loans with no specific allowance, interest income recognized in period	1	1	5
Impaired loans with no specific allowance, cash basis interest recognized in period	1	1	5
Home Equity Loans and Lines of Credit [Member]
Impaired loans with specific allowance, unpaid principal balance	5	8	6
Impaired loans with specific allowance, recorded investment	5	8	6
Related allowance
Impaired loans with specific allowance, average recorded investment	6	8	7
Impaired loans with specific allowance, interest income recognized in period
Impaired loans with specific allowance, cash basis interest recognized in period
Impaired loans with no specific allowance, unpaid principal balance
Impaired loans with no specific allowance, recorded investment
Impaired loans with no specific allowance, average recorded investment
Impaired loans with no specific allowance, interest income recognized in period
Impaired loans with no specific allowance, cash basis interest recognized in period
Commercial Real Estate Portfolio Segment [Member]
Impaired loans with specific allowance, unpaid principal balance
Impaired loans with specific allowance, recorded investment
Related allowance
Impaired loans with specific allowance, average recorded investment
Impaired loans with specific allowance, interest income recognized in period
Impaired loans with specific allowance, cash basis interest recognized in period
Impaired loans with no specific allowance, unpaid principal balance	32	336	34
Impaired loans with no specific allowance, recorded investment	32	336	34
Impaired loans with no specific allowance, average recorded investment	33	625	768
Impaired loans with no specific allowance, interest income recognized in period	1		156
Impaired loans with no specific allowance, cash basis interest recognized in period	1		73
Commercial Portfolio Segment [Member]
Impaired loans with specific allowance, unpaid principal balance	63
Impaired loans with specific allowance, recorded investment	63
Related allowance	63
Impaired loans with specific allowance, average recorded investment	31
Impaired loans with specific allowance, interest income recognized in period
Impaired loans with specific allowance, cash basis interest recognized in period
Impaired loans with no specific allowance, unpaid principal balance	40	555	39
Impaired loans with no specific allowance, recorded investment	40	555	39
Impaired loans with no specific allowance, average recorded investment	39	562	248
Impaired loans with no specific allowance, interest income recognized in period	1	1	74
Impaired loans with no specific allowance, cash basis interest recognized in period	1	1	74
Consumer Portfolio Segment [Member]
Impaired loans with specific allowance, unpaid principal balance
Impaired loans with specific allowance, recorded investment
Related allowance
Impaired loans with specific allowance, average recorded investment
Impaired loans with specific allowance, interest income recognized in period
Impaired loans with specific allowance, cash basis interest recognized in period
Impaired loans with no specific allowance, unpaid principal balance
Impaired loans with no specific allowance, recorded investment
Impaired loans with no specific allowance, average recorded investment
Impaired loans with no specific allowance, interest income recognized in period
Impaired loans with no specific allowance, cash basis interest recognized in period

Amount of allowance for credit losses related to recorded investment.

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Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Amount of average investment of impaired financing receivables for which there is no related allowance for credit losses.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 17
-URI http://asc.fasb.org/extlink&oid=118936363&loc=d3e5258-111524

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
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-SubTopic 10
-Section 50
-Paragraph 15
-Subparagraph (c)(1)
-URI http://asc.fasb.org/extlink&oid=118936363&loc=d3e5212-111524

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- Definition

Amount of interest income, recognized on accrual basis, on financing receivables that are recognized as impaired, for which there is no related allowance for credit losses.

+ References

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- Definition

Amount of interest income, recognized on cash basis, on financing receivables, for which there is no related allowance for credit losses and are recognized as impaired.

+ References

+ Details

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- Definition

Amount of investment in impaired financing receivables for which there is no related allowance for credit losses.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 14A
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=118936363&loc=SL6953550-111524

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- Definition

Amount of unpaid principal balance of impaired financing receivables for which there is no related allowance for credit losses.

+ References

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- Definition

Amount of average investment of impaired financing receivables for which there is a related allowance for credit losses.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 15
-Subparagraph (c)(1)
-URI http://asc.fasb.org/extlink&oid=118936363&loc=d3e5212-111524

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-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 17
-URI http://asc.fasb.org/extlink&oid=118936363&loc=d3e5258-111524

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- Definition

Amount of interest income, recognized on accrual basis, on financing receivables, for which there is a related allowance for credit losses and are recognized as impaired.

+ References

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Amount of interest income on financing receivables, for which there is a related allowance for credit losses, recognized on a cash-basis method of accounting that the financing receivables were impaired.

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- Definition

Amount of investment in impaired financing receivables for which there is a related allowance for credit losses.

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- Definition

Unpaid principal balance of impaired financing receivables for which there is a related allowance for credit losses.

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